Waveguide



Aug. 6, 1968 w. KRANK ETAL WAVEGUIDE Filed July 28, 1965 Fig. I

3 Sheets-Sheet 1 PRIOR ART Gexwayd SCVLCRLQ b own/L fittoma s Aug. 6,1968 w. KRANK ETAL 3,396,350

WAVEGUIDE Filed July 28,. 1965 3 Sheets-Sheet 2 Fig. 4

Fig. 5

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Aug. 6, 1968 w. KRANK ETAL 3,396,350

WAVEGUIDE Filed July 28, 1965 3 Sheets-Sheet 3 Inventors: \OoLfgcm KmnkUnited States Patent 3,396,350 WAVEGUIDE Wolfgang Kranlr and GerhardSchickle, Backnang, Germany, assignors to Telefunken Patentverwertungs-G.m.b.H., Ulm (Danube), Germany Filed July 28, 1965, Ser. No. 475,340Claims priority, application Germany, Aug. 6, 1964, T 26,745; Nov. 23,1964, T 27,467; Apr. 15,1965, T 28,397

16 Claims. (Cl. 333-95) ABSTRACT OF THE DISCLOSURE A corrugatedelliptical waveguide having a non-circular cross section and providedwith at least one recess extending in the longitudinal direction of thecorrugated guide and disposed symmetrically with respect to the minorcross-sectional axis of the guide for capacitatively loading the guidewithout substantially decreasing its mechanical flexibility.

The present invention relates generally to the micro wave art, and, moreparticularly, to a waveguide for transmitting linearly polarizedelectromagnetic waves of very high frequency and which can becontinuously produced.

Among the various conventional forms of waveguides, one form which iscalled the ridged waveguide is one in which the required dimensions aresubstantially reduced compared to those of a corresponding rectangularwaveguide, and this is accomplished by the capacity load provided byusing a ridge or cross-piece. With the same dimensions, the ridgedwaveguide has a higher limit frequency and a larger bandwidth.

Such a waveguide is shown schematically in FIGURE .1 as being formed bya rectangular waveguide 1 wherein the crosspiece or web 3 is arranged onone broad side a of the waveguide wall and disposed in the longitudinaldirection of the waveguide. The height of the web is always smaller thanthe short side b of the waveguide and the web is symmetrically arrangedin the cross section 2 of the Waveguide. This web can be formed by acorresponding recess in the broad side of the waveguide or by alongitudinal rod disposed interiorly of the waveguide. Consequently, theproduction of such a waveguide requires a larger expenditure than thosewhich are not loaded.

Also, a waveguide which can be wound on a drum, which is constructed ofa corrugated tube, and which has an elliptical cross section is alreadyknown.

It is the main object of the present invention to provide a novel loadedwaveguide which, for the same electrical characteristics hasconsiderable advantages regarding ease of production as compared toknown Waveguides.

Another object of the invention is to provide a device of the characterdescribed which is relatively simpler and less expensive inconstruction.

These objects and others ancillary thereto are accomplished inaccordance with preferred embodiments of the invention wherein awaveguide for the transmission of linearly polarized electromagneticWaves of very high frequency can be continuously produced. The waveguideis formed from a corrugated tube having a non-circular cross section andwherein the cross-section edges are free of abrupt changes of direction.The waveguide tube is welded and has a longitudinal seam. Thecorrugations are prefer-ably arranged in spiral fashion and at least onerecess or indention is provided in the direction of the axis of thewaveguide and symmetrically with respect to the minor axis thereof. Inaddition, the corrugation has a cross section which is approximatelysinusoidal, the distance between two successive corrugation ridges isbetween 0.1.

"ice

and 0.25 of the average free space wavelength of the frequency band tobe transmitted, the corrugation depth is 0.2 of the majorcross-sectional axis, and the length of that portion of the corrugationprofile which extends' interiorly into the waveguide is about 10% to 20%shorter than the length of that portion of the corrugation profile whichextends outwardly of the waveguide. 1

Additional objects and advantages of the present in.- vention willbecome apparent upon consideration of the following description whentaken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic perspective view illustrating a known waveguidearrangement.

FIGURE 2 is a schematic sectional view of a waveguide constructed inaccordance with the present invention and having a single recess.

FIGURE 3 is a schematic sectional view similar to FIGURE 2 but ofanother embodiment having a double recess.

FIGURE 4 is a schematic sectional view of a device similar to FIGURE 2but which is loaded with a dielectric.

FIGURE 5 is a schematic sectional View similar to FIGURE 3 but which isloaded with two dielectrics.

FIGURE 6 is a schematic partial longitudinal sectional view illustratingthe dielectric filling in the corrugation grooves.

FIGURE 7 is a view similar to FIGURE 6 illustrating a strip-likedielectric.

FIGURE 8 is a view similar to FIGURE 6 but wherein the dielectric fillsonly the bottoms of the grooves.

FIGURE 9 is a schematic elevational view of a section of a waveguidewherein various dimensions are shown for explanatory purposes.

FIGURE 10 is a schematic perspective view of a waveguide arrangementhaving the shape shown in FIGURE 2 and wherein a sheath is provided,with the protective sheath being broken away for purpose of clarity.

With more particular reference to the drawings, FIG- URE 2 illustratesan arrangement of a waveguide constructed in accordance with theinvention and wherein a longitudinally welded corrugated tube 4 isprovided. This tube has two cross-sectional axes a and b which aredisposed at right angles to each other and are of difierent length. Arecess 6 is provided in the longer wall of the waveguide and is arrangedto be symmetrical to the minor axis b of the cross section and extendsfor the entire length of the tube in a direction parallel to itslongitudinal axis. Thus, the cross section 5 of the waveguide is loadedby the recess 6.

As shown in FIGURE 3, the desired loading of the waveguide can also beobtained by using two recesses 9 and 10 which preferably are identicaland symmetrical to the minor cross-sectional axis and wherein the crosssection of the waveguide is approximately rectangular when the recessesare not taken into consideration. The shapes and sizes of the recessesdepend upon the individual electrical requirements. However, it must benoted that a deep recess decreases the flexibility of the waveguide. Itcan be seen that the waveguide tube 7 having the two cross sectionalaxes a and b is provided with the two recesses 9 and 10 as mentionedabove and which constrict the cross section 8 symmetrically with respectto the small axis b.

It should be noted that the present invention is not limited only to thecross-sectional shapes shown in FIG- URES 2 and 3, but can be used fordifferent cross sections. For example, it is possible to provide asquare, rectangular, round, or elliptical cross-sectional shape, that isthe shape not taking the recesses into consideration,

" since the recess'would clearly modify these cross-sectional w 3,forms. Also, the cross section can be arranged to be asymmetrical withrespect to at least one of the cross-sectional axes.

I When the, capacity loading of the waveguide is provided by twosymmetrically arranged recesses, then the edges of the cross section canbe provided in such a manner that they form a Cassinian curve. Such acurve has the following equation expressed in cartesian coordinates:

with the fixed points F F 030), whereby a is a constant and so that anoval with a recess according to FIGURE 3 is provided.

Depending upon the particular apparatus which need be connected to theend of the waveguide, it might be suitable to increase or reduce theload in the end portion and in the extreme case, it would not be loadedat all in order to provide as simple a transition as possible. This canbe taken into consideration at the time that the waveguide is producedby changing the recesses toward the end of the waveguide in a suitablemanner.

The waveguide can be wound on a drum and due to the load compared to theso-called ridged waveguide it has a larger bandwidth, or, at the samebandwidth, it has smaller dimensions.

The more the cross section of the waveguide deviates from the circularshape the greater is the disadvantageous recess influence on theflexibility of the waveguide.

As a further feature of the invention, the flexibility of the waveguidecan be increased by partially replacing the load provided by therecesses by an additional and dielectric load. This makes it possible touse smaller recesses, which increases the flexibility and thereby theusefulness of such a waveguide. On the other hand, if the bandwidth ismore important than the flexibility in a particular situation, then animprovement can also be obtained by the use of an additional load. Theload can be provided by means of a continuous dielectric member in theform of a flexible strip disposed parallel to the longitudinal axis ofthe Waveguide. The dielectric member preferably extends into the groovesof the corrugations of the waveguide profile.

FIGURE 4 illustrates a waveguide tube 11 having a recess 13 so as tomodify its cross section 12 as in the manner shown. An additional anddielectric load 14 is arranged within the waveguide so that the loadprovided by the recess 13 can be smaller.

FIGURE illustrates a waveguide 15 provided with recesses 17 and 18. Inaddition, two dielectric members 19 and 20 are arranged in the crosssection 16 and at the recesses.

As shown in FIGURE 6, the dielectric load 23 can be in the form of acontinuous strip or web which fills the corrugation grooves 24 of thewaveguide tube 22, and which extends parallel to the longitudinal axis21 of the waveguide tube.

7 FIGURE 7 illustrates a strip-like dielectrical load 28 arrangedparallel to the longitudinal axis 25 of the waveguide tube 26 and whichrests on the corrugation ridges 27.

Furthermore, the additional load can, when desired, be disposed atperiodic distances in the waveguide tube. As shown in FIGURE 8,dielectric elements 32 are disposed in a row or line which is parallelto the longitudinal axis 29 and extend into the corrugation grooves 31of the waveguide tube '30. The cross section of the load can be variedand this can be done in a manner which keeps the dielectric losses aslow as possible. Therefore, the load in the form of a dielectric memberis applied at those places where it is the most effective, that is, ifthe wave guide tube is provided with a recess, at the same place as therecess, or diametrically opposite the recess. If two recesses areprovided in the waveguide, then the dielectric load should be applied onone of these two recesses. Be sides the load being influenced by theposition and dimensions thereof, it is also influenced, as is known, bythe particular dielectric material which is selected in accordance withwhen'e is the eflective relative permittivity. p

.The dielectric load may be applied during the manufacturing of thewaveguide tube. The tube is normally constructed of a metalband which isbent into a circular cross-sectional shape and then longitudinallywelded. The smooth or even tube which is thus produced is then providedwith the desired corrugation and reshaped in cable-making machinery tohave the predetermined cross section. The dielectric coating or load canbe applied, during the continuous manufacturing process, on the bandbefore it is bent and this can be accomplished by gluing or spraying.The use of a foam dielectric such as tetrafluorethylene is preferablybecause of its flexibility.

In order to reduce interfering reflections of a wave fed into the deviceon the corrugation profile the corrugation can be approximatelysinusoidal. The distance e as shown in FIGURE 9 between two corrugationridges is between 0.1 and 0.25) where A is the awerage wavelength infree space of the frequency band which is to be transmitted. The depthof the corrugation t is smaller than 0.2 of the length of the majorcross-sectional axis which is a in FIGURE 2. The length 0 of theportions 32 of the corrugation which extend downwardly or interiorlytoward the waveguide tube is arranged to be 10 to 20% shorter than thelength d of the portions 33 of the corrugation which extend outwardly.

When the waveguide tube is provided with spiral type corrugation, thepitch of the corrugations should be between 5 and 15 and 8 has proved tobe a preferred value.

When the corrugations are arranged to have a profile of the typedescribed above, a sufiicient flexibility of the waveguide is assuredand at the same time the reflection factor is considerably decreasedwith respect to conventional devices. Thus, there is provided a flexiblewaveguide which can be quickly assembled and which can be used for thetransmission of wide bands. Since the waveguide can be continuouslyproduced and can be wound on a drum, the waveguide is particularlysuitable for use as an antenna feeder line and in assembling mobilestations. Attenuation and reflection characteristics are com.- parableto rigid or non-flexible waveguide arrangements.

In order to avoid mechanical damage to the waveguide and at the sametime to provide protection against corrosion, a non-abrasive plasticsheath or coating can be provided about the waveguide which can be apolyisobutylene mixture with graphite added. Such an arrangement isshown in FIGURE 10 wherein a protective coating 35 is provided on acorrugated waveguide 34.

In the production of this device, it is preferable to deform alongitudinally welded corrugated tube having a circular cross section ina continuous process in a swageing device until the desired crosssection is obtained. Subsequently, the corrugated tube is treated byplastic extruding devices which provide a plastic covering which fillsthe grooves of the corrugation.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes, andadaptations, and the same are intended to be comprehended within themeaning and rangeof equivalents of the appended claims. a

What is claimed is:

1. A continuously produceable waveguide arrangement for the transmissionof linearly polarized waves of very high frequency comprising acorrugated tube welded longitudinally and having a non-circular crosssection provided with corrugations, and having at least one recessdisposed in the longitudinal direction of the corrugated tube andarranged symmetrically with respect to the minor cross-sectional axis,wherein the corrugation has a cross section which is approximatelysinusoidal, the distance between two successive corrugation ridges isbetween 0.1 and 0.25 of the average free space wavelength of thefrequency band to be transmitted, the corrugation depth is 0.2 of themajor cross-sectional axis, and the length of that portion of thecorrugation profile which extends interiorly into the waveguide is aboutto shorter than the length of that portion of the corrugation profilewhich extends outwardly of the waveguide.

2. An arrangement as defined in claim 1 wherein the entire waveguidedevice is symmetrical with respect to the minor axis of the crosssection.

3. An arrangement as defined in claim 1 wherein the corrugations are inspiral form.

4. An arrangement as defined in claim 1 wherein two recesses areprovided which are opposite each other.

5. An arrangement as defined in claim 4 wherein said recesses areidentical.

6. An arrangement as defined in claim 1 further comprising at least onedielectric load which extends parallel to the longitudinal axis of thewaveguide.

7. An arrangement as defined in claim 6 wherein said dielectric load isprovided by a continuous flexible dielectric member.

8. An arrangement as defined in claim 7 wherein the dielectric loadfills the corresponding corrugation grooves of the waveguide profile.

9. An arrangement as defined in claim 7 wherein the dielectric member isin strip form.

10. An arrangement as defined in claim 6 wherein said load is providedby dielectric elements disposed at periodic distances from each otherand which are arranged in the corrugation grooves.

11. An arrangement as defined in claim 6 wherein there is a singlerecess and said dielectric load is disposed symmetrically with respectto the minor crosssectional axis.

12. An arrangement as defined in claim 11, wherein said dielectric loadis disposed along said recess.

13. An arrangement as defined in claim 11, wherein said dielectric loadis disposed opposite said recess.

14. An arrangement as defined in claim 6 wherein there are two recessesand the dielectric load is provided at least at one of the recesses.

15. A waveguide arrangement for the transmission of linearly polarizedwaves of high frequency comprising a corrugated tube having anon-circular cross section, the corrugations being approximatelysinusoidal and the distance between two successive corrugation ridgesbeing between 0.1 and 0.25 of the average free space wavelength of thefrequency band to be transmitted, the corrugation depth being 0.2 of themajor cross-sectional axis, and the length of that portion of theprofile extending interiorly into the waveguide being about 10 to 20%shorter than the length of that portion of the corrugation profile whichextends exteriorly thereof, said arrangement further comprising anon-abrasive plastic covering disposed over said tube.

16. A waveguide arrangement as defined in claim 15 wherein thecorrugations are arranged to be in spiral fashion and the pitch of thecorrugation is between 5 and 15.

References Cited UNITED STATES PATENTS 1,996,186 4/1935 Aifel 333-2,563,578 8/1951 Candee 333--95 2,590,511 3/1952 Craig et al. 333-952,632,805 3/1953 Vogeley et a1. 33395 2,675,832 4/1954 Hamilton 333-953,090,019 5/1963 Johnson et a1. 333-95 3,200,356 8/1965 Shuttloifel eta1. 33395 3,299,374 1/1967 Schickle et a1 33395 FOREIGN PATENTS 877,6929/ 1942 France.

739,488 11/1955 Great Britain. 1,061,850 7/1959 Germany.

425,104 9/ 1947 Italy.

OTHER REFERENCES New Flexible Heliax Waveguide, Andrew, Bulletin 8529,received February 1964.

HERMAN KARL SAALBACH, Primary Examiner.

L. ALLAHUT, Assistant Examiner.

